Per your previous writing about "common sense" and concepts that "slither out of people's mental grasp", can a series of speakers set up around a racetrack and playing the sound of a car actually create the same Doppler effect as the actual car did?

Ron

No, they can't.

The Doppler effect happens when a moving object emits something, in this case sound waves. When each new wave is emitted in front of the sound source, it's closer to the previous wave than it would have been if the emitter were stationary. Behind the emitter, each new wave is a bit further from its predecessor than it would be if the emitter weren't moving.

We don't notice redshift or blueshift in everyday life because Doppler shift is a proportional effect, and the speed of light is so high that no light-emitter that humans normally deal with moves at an appreciable fraction of lightspeed relative to us. The speed of sound, however, is relatively low (about 340 metres per second close to standard temperature and pressure), and the human ear is quite sensitive to changes in pitch. So we can easily hear this effect on the sound of a car engine...

...or horn, when that car passes us at speed.

(My favourite example of car-horn Doppler shifting, which includes a lot of moderately comprehensible cursing, is this one.)

If you set up a bunch of speakers to imitate the sound of a passing car, none of them are moving, so there will be no Doppler shift from the point of view of a stationary observer. You could create the same effect by deliberately adding pitch shifts to the sound being played so that it sounds correct from a given listening location, but that'll make it sound wrong to listeners somewhere else. Doppler changes are caused by waves being bunched up and spread out by motion, and that just doesn't happen if neither listener not sound-emitter are moving. There's nothing about the order in which speakers play sounds that change what the sounds are.

(OK, there might be some interference effects audible at various listener locations. But that wouldn't sound Doppler-y.)

There actually would be Doppler effects if you were in your own car driving around the racetrack during the ghost-of-Senna performance, though. A moving listener creates Doppler shift in exactly the same way as a moving source:

A related concept to this is the idea of the faster-than-light laser dot.

Consider flicking the dot of a laser pointer across, say, the face of the moon. (Presume you've got a laser that's well enough collimated that it still has a small dot at that distance.)

If the dot crosses the moon in, say, a hundredth of a second, and even if you ignore its curvature the moon is about 3,400 kilometres across, then that dot is going about 340,000 kilometres per second, which is faster than light. Address for delivery of Nobel Prize in Physics will be provided on request.

Unfortunately, and to the chagrin of a great many cats, a laser dot is not a "thing". It's just where photons happen to be falling and bouncing off at any given moment. Moving a dot faster than light is indeed perfectly theoretically possible, but you might as well give two blokes each a flashlight with an accurate timer built in, have them synchronise timers and then move a thousand kilometres apart, and then turn their flashlights on and off so that one light-pulse happens a thousandth of a second before the other. Presto, now a dot has moved at a million kilometres per second, more than three times the speed of light!

Except that doesn't mean anything, because that dot of light is not a thing moving faster than light. You could fill the space between those two flashlights with a trillion more flashlights timed to give a wonderfully smooth movement of the dot, but the dot would still not be a thing travelling faster than light. A spinning lawn sprinkler may have a contact point between droplets of water and the circumference of its spray pattern that goes round and round at a quite impressive speed, but that's just where the water hits the lawn, it's not an actual separate moving object.

(By the way, smart alecks, relativistic time dilation does not mean the flashlight timers would get significantly out of sync if the flashlight-carrier on one end got to his assigned location on foot, taking weeks, and the other got to his by rocket-sled at ten thousand kilometres per hour. At 10,000km/h your clock willtick slower than that of a stationary observer, but only by a factor of 1.0000000000429. The fastest object humanity has ever made is the Helios 2 probe, at 70,220 metres per second relative to the sun; it achieved a time dilation factor all the way up at 1.000000027!)

A further extension of this idea is to say, "OK, what if I've got a stick a million kilometres long, and I hold one end of it and spin it around my head in a circle in, say, five seconds? The circumference of a circle with radius one million kilometres is 6,283,185 kilometres, and the tip of the stick it will go all the way around that circumference in five seconds, which is 1,256,637 kilometres per second. The tip of the stick is a thing and not just a dot of light, so it's really going at that speed, which is 4.2 times the speed of light, NOW can I have my Nobel prize?"

No, you still can't.

Ignoring the obvious issues regarding the construction and inertia of a million-kilometre broomstick, there is no way for one end of an object to know what's happening to the other end at faster than the speed of light. Motion of the object occurs when the molecular bonds that hold it together are stretched and pull the molecules along, and there's nothing about those molecular bonds that causes them to influence each other faster than light. Otherwise you could make an instantaneous communication system by taking your very long magic broomstick and tapping on the end of it in Morse code or something.

So even if your very long stick were made of alien indestructium with an infinite tensile strength, spinning the middle of it round and round would just cause the whole thing to start wrapping up into a spiral. You could then try cracking it like a whip if you wanted, because you're Cowboy Galactus or something, but the other end of the object would still not travel faster than light, because no "information" within the object, in this case the information regarding the location and motion of its component particles, can travel faster than light either.

This seems bizarre, but again this is because we're talking about scales far larger than those on which humans normally operate. On the very large scale, nothing is particularly solid. If planets and stars and even galaxies run into each other, the energies involved may be unimaginably large, but all of the actual objects behave pretty much as if they were made of blancmange.

If Unicron were actually the size of even a smallplanet, no material that even theoretically exists in the universe would be stiff enough for him to be able to transform like his car-sized distant relatives. (Well, maybe if he's made of some kind of degenerate matter and has magical technology to prevent himself from collapsing into a black hole. Once you can cancel gravity, you might as well move information faster than light, too. It never seems to take a Transformer or Decepticon much more than twenty minutes to get to anywhere in the universe, after all.)

To reward anybody who managed to get to the end of this post, the ghost-of-Senna ad sounds pretty good, but the Shell-Ferrari one from a few years ago is much better:

(I think that version's the best one on YouTube in both resolution and sound. Aspect ratio's wrong, though.)

Do you know the odds of getting electrocuted if one is standing in a wet shower with wet skin using a cordless (battery-powered) sander? I don't know what kind of power I'll need to work on residential showers for hours at a time, but the electric chorded sander I WAS using (until I decided that I'm tired of risking electrocution) says it's a 120 Volt, 10 Amp model.

Jennifer

There's probably no danger, but there could be some.

Cordless tools all run from low-voltage DC, although the voltage has risen in recent tools that use one or another flavour of rechargeable lithiumbattery. Higher voltage is better, from the tool-makers' point of view, because a given power from a higher voltage requires less current. This means thinner wires, less beefy switches, and generally speaking a cheaper, lighter tool with the same power.

Cordless tools are also, in general, significantly less powerful than corded versions. It's normal for corded drills and saws and sanders and such to draw peak power of at least several hundred watts. The ten-amp 120-volt rating of the sander you mention makes it a 1200-watt unit (so I presume you're talking about a belt sander, not an orbital one), though it'll only draw that much when it's working hard. You can expect even big heavy cordless tools to have no more than half the power rating of a similar corded tool.

Discovering exactly what that rating is can be difficult, partly because cordless tools can have a larger range between their "spinning freely doing nothing" and "working so hard it's barely turning at full power" power consumption than corded tools do. Mainly, though, cordless power ratings are harder to find because consumers think more watts are always better. So a cordless tool that costs three times as much as the wall-powered version, yet has a third the power rating, won't sell well, unless the manufacturer conceals that latter number.

I'm telling you all this just to explain my original wishy-washy "possibly dangerous" statement. If you're using a 12V tool then you probably won't be able to do yourself any electrical harm with it, even if you smash the thing on the wall until it breaks and then smack yourself in the chest with the pointy bits.

A 36-volt tool, on the other hand, is edging up toward the kind of voltage that actually can harm you, if only indirectly. (Direct harm: Current through your heart stops it, you die. Indirect harm: Current through some other part of your body causes you to spasm and dig a tool into yourself, fall off a ladder, flop out of the shower recess and smack your head on the toilet, et cetera. This sort of secondary injury following a non-fatal shock is a lot more common than injury or death caused directly by electricity.)

In the real world, even crappy bargain-basement cordless tools have enough plastic between you and the wiring battery terminals that no matter what voltage they run at, you pretty much have to make a specific and deliberate project out of killing yourself with one. Working in a wet environment is still dangerous, but only because it makes it easier to slip and then drill, saw or sand yourself instead of the workpiece.

Brand-name tools are generally safer still, and adding water to the situation may ruin the tool but is unlikely to hurt the user. Even the commonly-recognised-as-lethal "dropping a hair-dryer into your bath" situation is actually not terribly likely to kill you, though I don't recommend you try your luck.

If it's possible to electrocute yourself with cordless-tool gear in any way at all, here is I think your best chance of doing it without specifically running wires from the inside of the tool to nails driven into your chest. There are plenty of battery designs with exposed terminals of one kind or another, so suppose you eject the battery from the tool by accident, and then somehow grab that battery with both, wet, hands, so positive is touching one hand and negative is touching the other.

Even then, the resistance of human skin is way up in the tens of thousands of ohms - I found the resistance between two closely-spaced points on my tongue to be 70,000 ohms. So even with a 36-volt battery it'd be surprising if one whole milliamp managed to flow across your chest, and not all of that would go through your heart. I think you'd be an easy order of magnitude away from enough current through the heart for there to be any risk at all.

(I'm sorry to say that I'm not about to conduct heart-stopping experiments on myself. I have, however, previously zapped my arm for science.)

If both of your hands had bleeding cuts on them then 36 volts might be enough to at least give you a shock you could feel and it might have cardiac consequences, but this is really pushing it. And any sort of work gloves not made of chain-mail would erase the risk completely.

And, of course, back in the real world it continues to be downright difficult to actually touch the positive with one hand and the negative with the other. If you just grabbed both terminals of a 36-volt battery with one wet bleeding skinless lightly-salted hand then it'd sting like a bugger, but once again the only real health risk it'd present would be if the pain startled you enough that you then hurt yourself in some other way.

I won't be surprised if cordless-tool voltages rise further, though. There are already cordless mowers that run from 48-volt packs, for instance. So it's possible that a few years from now there'll be cordless tools running from voltages high enough to pose real electrocution risks.

It'll still be a lot less dangerous than it was in the olden days of corded tools, though, when casings were still commonly made of shiny cast aluminium. Then, the user's life was in the hands of the manufacturers and electricians who're meant to keep earth wires connected, and prevent live wires from touching the tool chassis.

With modern plastic casings and other construction improvements, even a theoretical 96-volt cordless tool is not likely to be an electrocution risk, even if you use it in the rain or, more realistically, get all hot and sweaty while working.

There's a lot of energy in a cordless-tool battery, though, and they definitely can hurt you if that energy is released very quickly because of, say, a short circuit...

...or severe over-charge...

...or physical damage...

The reason why drills and laptops and iPads aren't exploding all over the place is that the naturally excitable personality of lithium-ion technology, in particular, is kept calm by strong casings and protection circuitry ranging from simple fuses to smart current limiting:

If one of your cordless tools manages to puncture the battery of another, though, your life may still become quite exciting.

So I suppose I've allayed your fears of one kind of injury and then given you a new one to worry about.

It is not a big fan. The diameter of the see-through rubbery blades when they're spinning is about seven centimetres (2.75 inches). The blades fold back at rest, and can thus get in the way of the crank a bit on start-up.

The blades spin fast, though; they're heavily geared-up, and turn something in the order of 110 times per crank of the handle.

I think this fan may actually have a substantial calories-expended-to-air-moved advantage over a simple paper fan. Both cool your face while they warm up your arm muscles, but I think the crank-fan requires less effort.

It also takes up less room, both in your bag and when you're using it.

I wouldn't expect this plasticky little thing to last a whole summer of frequent use, though. But it's probably more durable than similarly tiny fans that run off batteries or USB power; no motor brushes to wear out or solder joints to let go.

I think the principal purpose of this device is to make other people smile when you use it, though, and on that count it seems entirely successful.

And yes, you can turn it to point away from you and crank the handle the other way, and run about pretending you're an aeroplane.

EDIT: I just opened it up.

Black plastic gears on metal shafts, and a couple of actual bushings for the output shaft. The bushings are only plastic too, but should wear slower than if there were only holes in the casing plastic for the fan-shaft to go through. This trinket was not just thrown together.

(The gears were dry; I added some fancy plastic-safe oil, and now I think the fan turns more quietly. This may be a complete fantasy.)

(DealExtreme have bulk-buy discounts as well; you pay an extra $US1.70 for the whole order to use the "Bulk Rate" feature, then pay less for three or more of any given item in that order. The three-unit prices for these fans are only two cents more than the ten-unit prices.)

...of an impressive piece of antique finger-grabbing agricultural equipment, and suggested it as another illustration for the "pulley paradox". Again, if you don't know about crowned pulleys, contraptions like this look offensively impossible.

As a weekend project, I suggest commenters point to the most belt-and-pulley-infested machinery they can find on the Web.

I am also pleased to note that unless the corporate copyright enthusiasts manage to extend terms yet again, the works of W. Heath Robinson should pass into the public domain at the end of 2014.

(A few works illustrated by Robinson are already in the public domain, but I don't think any of the stuff for which he's most famous is, yet.)

I was watching "Industrial Revelations" on Discovery, and I noticed a lot of Industrial Revolution factories running from one power source, a steam engine or waterwheel, with power distributed via a load of parallel overhead shafts, which brief Googling tells me are called line shafts. A belt runs from each shaft to each working machine, often with a free-turning wheel next to the one that drives the machine so the belt can be moved over onto the free wheel to "turn the machine off".

What I can't figure out is, what kept the belts on the wheels? They don't have ridges on the edges to contain the belt, they're not V- or U-profile with a matching belt shape, they're just flat metal as far as I can see, yet the belts don't fall off.

Traditional flat leather drive belts were a pretty good piece of technology. They weren't even as much of a death-trap as you might think just looking at them, since they often had enough slack that getting some piece of yourself or your clothing caught between belt and pulley wouldn't necessarily whip you into the air or smash your face into the machine. Getting your hand caught in the moving parts of the steam engine or waterwheel gearing on the other end of the lineshafting system was bad, bad news, but if only a belt had grabbed you, you had at least a fighting chance of yanking yourself free. There usually wasn't even enough pressure between belt and wheel to instantly crush your hand.

On all but the biggest of the Towers-of-Hanoi stepped sections of that pulley, the belt can only fall off on one side. But where's the power for the stepped pulley coming from? Another dang flat pulley, that's where!

...you can just about see that the pulley surface profile is slightly convex, or "crowned". The profile of the pulley is sort of like that of a wooden barrel, except less pronounced.

Wherever a flat belt is on a crowned pulley, it will tend to move towards the centre. This effect is reliable enough that some of the pulleys in a flat-belt power-transfer arrangement actually can be completely flat, as long as every belt runs over one or more crowned pulleys somewhere else.

For practical purposes, you can stop here. Slight convex profile to pulley equals flat belt staying in the middle of the pulley. Provided all other pulleys are well enough aligned, at least; if the pulleys aren't lined up very well then even if all of them are crowned, the belt may still "walk" off one of them. But basically, crowned pulleys equals centred belts.

If you want to know why crowned pulleys work as they do, things get a little more confusing. Confusing enough, actually, that the question can be presented as a puzzle, or even as a "paradox".

The edge of a flat belt that is closest to the middle of a crowned pulley will be stretched a little more than the other edge of the belt, because the crowned pulley has a greater diameter in the middle. This gives the belt-edge toward the middle of the pulley higher tension and thus more traction than the other edge. So wherever the more tense, higher-traction portion of the belt wants to go, the whole belt will tend to go.

Any given point on the portion of the belt in contact with a pulley will, by definition, contact a point on the pulley. But when the pulley is crowned and the belt is not in the middle of it, the slight bend in the belt means a point on the tenser side of the belt, closer to the middle of the pulley, will be unable to stay in contact with the same point on the pulley as it rotates. The slight bend in the belt created by the crown profile points the belt away from the middle of the crown profile. All parts of the belt in contact with a pulley "want" to stay in contact with that same part of the pulley - that's sort of the whole point of friction belts on pulleys. But because the tenser edge of the belt, closer to the middle of the pulley, has more grip than the other edge, the whole belt tends to climb to the middle of the pulley.

This illustration from The Elements of Mechanism, which I found on this page explaining the aforementioned "paradox", may help you visualise this. It certainly helped me. The point on the pulley (in this case two truncated cones, not a smoothly curved crown) which is under point "a" on the belt will end up at point "b" as the pulley rotates. The belt tries to stay frictionally stuck to the same part of the pulley, so it climbs to the middle.

(A "perfect" crowned pulley with a smooth curve is a bit of a nuisance to make, so some crowned pulleys have a flat centre and curved, or even conical, ends, and some are as shown in the above picture, just two truncated cones stuck together base-to-base. These designs don't work as well - a belt will wander on the flat part in the middle of the first type, and the ridge in the middle of the second type reduces grip and wears the belt - but they work well enough for many purposes.)

The crowned-pulley effect isn't very strong unless the crown shape is very pronounced, which would make the belts wear out quickly; this is why it can't compensate for more than slight misalignment of the pulleys. Pulleys with raised edges of one kind or another - including V-profile belts and pulleys and their relatives - can tolerate much more misalignment.

(An exaggerated crown shape does make the crown effect much easier to see, though. Famous Web-woodworker Matthias Wandel has a page about the crown effect too, that includes an exaggerated pulley.)

Although the era of lineshafting has long passed in the Western world, flat belts and crowned pulleys survive as conveyor belts, and in the strangest other places - the paper-handling machinery in photocopiers, for instance!

You can also set up a model steam engine to run a whole model machine shop via tiny line shafts. Most such setups, however...

...and is attempting to have a metal model made so its input and output power can be tested.

What do you think of the concept, and can you tell how on earth it works? I'm still trying to figure out how this is too different from CVT, other than maybe a wider range.

I'm still wondering if this is somehow impossible, but personally I'm open to the possibility that it's a similar step such as CVT and the in-article claims are typical science-journalism overestimations.

Fortunately, though, an infinitely-variable transmission (IVT) is not actually in any way related to perpetual motion. All it is, is a continuously-variable transmission (CVT) that has some way to run its variable "gear ratio" all the way down to infinity-to-one, also known as a "driven neutral".

(This is, by the way, not the same as just running the gear ratio up so much, billions or trillions to one, that the final gear in the train is functionally immobile, and could be embedded in concrete without having any effect on the load of the driving motor for some years. A true "driven neutral" could be driven at a trillion RPM for eleventy frajillion years, and never turn the output at all. A transmission that bottoms out at zillion-to-one gearing would, however, be perfectly usable as a real-world infinitely-variable transmission.)

Because it can gear down to infinity-to-one, this does indeed mean that this transmission doesn't need a clutch, which does indeed reduce complexity. Whether a real-world version of the D-Drive would be too big or too heavy or inadequate in some other more complex way for real-world duty, though, I don't know. But there's nothing crackpot-y about the basic idea.

As the video makes clear, the big deal here is making an IVT - actually, a mere CVT, that still needed a clutch, would do - that uses standard gearbox-y sorts of components, or can in some other way handle lots of power and torque without being unmanageably big, expensive and/or quick to wear out.

Normal CVTs have been available in low-torque machinery like motor-scooters for some time, and are now showing up in some mainstream, full-sized cars as well. But they're still a fair distance from ideal.

It's easy to make a CVT, you see. Here's one made out of Lego. It's hard to make a CVT that can handle lots of power. And yes, the fact that most CVTs contain some sort of friction-drive device is a big part of the reason for this.

Note, however, that there's a big difference between dynamic-friction CVTs like this one or the Lego one, in which friction between moving parts transfers power, and static-friction CVTs like this one, in which friction locks components together (as in a clutch!), and they don't wear against each other.

But even here, real-world elements muddy the water and make it hard for someone who doesn't actually work at the engineering coalface to tell whether they're looking at something genuinely new and useful, or something that's not new at all, and/or won't work. Here, for instance, is the NuVinci transmission, a friction-based CVT that spreads the friction stress between numerous relatively lightly-clamped spheres - it's related to the "ball differential" with which R/C car racers are familiar. The NuVinci's makers claim it's useful for high-power, high-torque applications. And maybe they're right. I don't know.

For an excellent example of the ugliness that can happen when somewhat specialised knowledge is repurposed by people who, at best, don't know what they're talking about, look at this particular piece of "water-powered car" nonsense, where the well-known-to-jewelers electric oxyhydrogen torch is claimed to be some sort of incredible over-unity breakthrough. This sort of thing happens all the time - it's just, usually, not quite such a blatant scam.

As the Gizmag article mentions, many commercial CVTs are also deliberately hobbled by car manufacturers. They force the transmission to stick to only a few distinct ratios, and also to want to creep forward when at rest, just like a normal automatic transmission. This isn't a limitation of existing CVT technology, though; it's just deliberately bad implementations of it.

(The manufacturers do this so that people who're used to normal autos won't be freaked out by a CVT. Those of us who'd like the superior technology we pay for to be allowed to actually be superior just throw up our hands, and cross those cars off the worth-buying list.)

I think one trap for the D-Drive could be the second motor that handles the ratio-changing - that might need to spin really, really fast in certain circumstances.

There's also the fact that this is only really an infinitely-variable transmission at one end of the ratio scale. The D-Drive can gear down an infinite amount, and right on through zero to negative (reverse) ratios. But unless I'm missing something, I don't think it can gear up at all. So the output shaft can't ever turn faster than the input shaft. This is a problem if you want to do low-power flat-highway cruising, when the engine's turning quite slowly but the wheels are turning very fast.

Normal cars have significant gear reduction in the differential, though - the "final drive ratio". Perhaps if you make the diff a 1:1 device, which shouldn't make it that much bigger, the D-Drive's output-ratio limitation won't matter.

The reason why I'm saying "might" and "perhaps" so often is that I, like the New Inventors judges, am not actually an expert on the very large number of mechanisms that the human race has invented over the centuries. The simplicity of the D-Drive makes me particularly suspicious. The D-Drive's mode of operation may be a little difficult for people who don't work with mechanisms all day to intuitively grasp, but there aren't many components in there, and none of them are under 100 years old. Actually, that's probably a considerable understatement; I'm not sure when epicyclic gearing became common knowledge among cunning artificers, but I can't help but suspect that a master clockmaker in 1650 wouldn't find any of the D-Drive's components surprising.

Sometimes someone really does invent some quite simple mechanical device, like the D-Drive, that nobody thought of before. But overwhelmingly more often, modern inventors just accidentally re-invent something that was old when James Watt used it.

To get an idea of the diversity of mechanical movements and mechanisms, I suggest you check out one of several long-out-of-copyright books full of the darn things. I think Henry T Brown's 507 Mechanical Movements, Mechanisms and Devices is the most straightforward introduction; it's a slim volume available for free from archive.org here.

(If you'd like a paper edition, which I assure you makes excellent toilet reading, you can get the one I have for eight US bucks from Amazon. Here's a version of it for four dollars.)

And then there's Gardner Dexter Hiscox's Mechanical movements, powers, devices, and appliances, whose full title would take a couple more paragraphs, which is also available for free.

Both of those books carry publication dates in the early twentieth century, but many of the mechanisms in them were already very, very old. Like, "older than metalworking" old. But several of them are still, today, unknown to practically everybody who's not able to give an impromptu lecture about the complementary merits of the cycloidal and Harmonic drives.

(You may, by the way, notice rather a lot of mechanisms in those old books that do the work of a crank. That's because one James Pickardpatented the crank in 1780 - plus ça change. This forced James Watt, and many other early-Age-Of-Steam engineers, to find variably practical Heath-Robinson alternatives to that most elegant of mechanisms to get the power of their pistons to bloody turn something. Watt's colleague William Murdoch came up with a kind of basic planetary gearing to replace the crank. Planetary gears have, in the intervening 230-odd years, found countless applications - including the D-Drive!)

Getting back to Mr Durnin and The New Inventors, they both currently allege that the D-Drive is a "completely new method of utilising the forces generated in a gearbox". According to this Metafilter commenter and this patent application, that may not actually be the case, since 18 of the 19 formal Claims made in the application appear to have been turned down. But, again, I could be getting this wrong, because somewhere behind the impenetrable thicket of legalese I suspect the "Written Opinion" may be saying that the final Claim actually is patentable as a separate worthwhile thing. (See also this forum thread.)

This all has me thinking, again, about the repeatedly-demonstrated gullibility of The New Inventors. When I can bring myself to watch the show, I keep thinking - OK, actually sometimes shouting - about how I'd spoil the party by asking at least one out of every four inventors "would you be willing to make a small wager that your device is not fundamentally worthless, or a duplicate of something that's been in production for years?"

(Sometimes, I'd just say "Have you always dreamed of being a rip-off artist, or is it a recent career development?")

The New Inventors seem to not have much of a peer-review system to keep the show free of crackpots, scammers and ignorant inventors who're unaware that their baby was independently invented in 1775. Or maybe there's just a shortage of interesting inventions, like unto Atomic magazine's shortage of interesting letters, so they let even the dodgy ones onto the show as long as they look impressive.

Perhaps the people on the judging panel just studiously avoid saying anything that might attract legal action from an inventor outraged that someone dared to point out that his magic spark plugs strongly resemble 87 previous magic spark plugs out of which the magic appeared to leak rather quickly.

It doesn't even take a lot of searching to find other IVTs. Here's one that, like the D-Drive, has no friction (or hydraulic) components. Its highest input-to-output gear ratio is quoted as "five to one", which is weirdly low; perhaps it's meant to be the other way around.

I hope, I really do hope, that the D-Drive turns out to be a proper new and useful device. We can always use another one of those.

But I remain very unconvinced that something this simple, aiming to do this straightforward a task, really is useful, let alone new.

To summarise: The D-Drive does not remove all friction components from the drivetrain, because it can only ever be a part of that drivetrain, and needs supporting stuff that'll probably need friction components. And yes, it would need a motor just as powerful as the "main" one to drive the control shaft.

And Steve Durnin is apparently proud of independently coming up with a system similar to Toyota's Hybrid Synergy Drive "Power Split Device". I must be missing something, there, seeing as if this is the case then the D-Drive probably isn't patentable, and probably wouldn't even be particularly marketable.

I think quite a lot of the other There, I Fixed It posts have a similar charm, especially to people like me who actively prefer shabby things to shiny ones. (I am not being sarcastic when I say cat-scratches "improve" furniture.) I like things that look totally ramshackle, or even obviously broken, but actually work, or can pretty easily be made to work.

You could make it properly structurally sound, too. Just gather enough unimportant documents - not, I think you'll find, a difficult task for many people - and pile them up one sheet at a time, putting a circle of white glue on each sheet. Then put the desk or something back on top of the pile to clamp it while the glue dries.

You could make a desk that stood on four of these things, a coffee table on four short ones, a single one as a display plinth for yourOfficeSpacecollectibles...

You could even make the stack lightweight, if you did something like core out the middle inside the glue-rings and replace it with a length of large-diameter PVC pipe. And then you could, of course, hide booze in it!

I invite readers to nominate their own examples of constructions and contraptions in this sort of improbable-yet-functional, broken-yet-working category.

(With pictures, if possible! Commenters can't use image tags, but if you just put the URL of the image, Flickr page or whatever in your comment I'll picturify it, provided it doesn't make my Civil Defense Lemonparty Survey Meter beep too loudly.)

This is a system used in real factories, to reduce the machinery needed to handle different goods, or the same goods at different stages in the manufacturing process. Note that the cylinders and the cubes don't mix.